It's a "busy" sentence anyway (without even knowing what comes before your first comma), so I would keep "that" to make it easier for the reader to parse.
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FumbleFingersOct 20 '11 at 15:59

It seemed a bit more fluid without out it, but, yes, it makes it easier to parse. The 'comes before' part is busy too. In essence, 'Your sessions are great. I have found another person, and I want to advise they, too, come.'
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Bobbi BennettOct 20 '11 at 16:14

I don't really think it's really a matter of "grammaticality". In Shakespeare's King Lear, Act 4, Scene 5 we have Therefore I do advise you, take this note, where I don't think the comma makes any difference (nor did Samuel Johnson in the link).
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FumbleFingersOct 20 '11 at 17:24

I think the comma does make a difference, but I see what you mean about Johnson. It appears that it was grammatical in Johnson's day, but I do not find it so now.
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Colin FineOct 21 '11 at 11:21

1

Perhaps we have different ideas on what "grammatical" means. All permutations (that before you, or to/comma/nothing after it) seem grammatical to me. Some might be dated or otherwise unusual, but really that's all just style.
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FumbleFingersOct 21 '11 at 13:43